Internalization of Adenovirus by Alveolar Macrophages Initiates Early Proinflammatory Signaling during Acute Respiratory Tract Infection

Abstract

Adenovirus is a common respiratory pathogen which causes a broad range of distinct clinical syndromes and has recently received attention for its potential for in vivo gene delivery. Although adenovirus respiratory tract infection (ARTI) results in dose-dependent, local inflammation, the pathogenesis of this remains unclear. We hypothesized that alveolar macrophages (AM) rapidly internalize adenovirus following in vivo pulmonary administration and then initiate inflammatory signaling within the lung. To evaluate the role of AM in the induction of lung inflammation during ARTI in vivo, we directly assessed adenovirus uptake by murine AM and correlated uptake with the initiation of proinflammatory gene expression. Adenovirus, a nonenveloped DNA virus with at least 45 serotypes, is an important respiratory pathogen affecting individuals of all ages and accounting for 7 to 10% of all respiratory illnesses in infants and children, with an incidence of between 5 to 10 million infections annually in the United States alone (13, 21). Adenovirus respiratory tract infection (ARTI) occurs sporadically, epidemically, and nosocomially, presents in a wide spectrum of distinct clinical syndromes ranging from self-limited acute pharyngitis to fatal pneumonia, and has been identified as an etiological factor associated with exacerbations in individuals with chronic obstructive lung diseases (13). Despite the frequency and broad range of clinical presentations, the pathogenesis of inflammation in ARTI is poorly understood. Early information regarding host responses to adenovirus was derived from efforts to develop human adenovirus vaccines (42) or to understand the pathology of fatal adenoviral pneumonia (4). Recently, ARTI has been studied in a variety of animal models, including mice (14, 37, 58), Cotton rats (Sigmodon hispidus) (15, 39, 59, 60), and primates (8, 44, 55, 61) as part of preclinical toxicology studies for human gene therapy clinical trials for cystic fibrosis (reviewed in references 7 and 48). Studies in humans showed that administration of replication-deficient adenovirus vectors to the respiratory tract can cause dose-dependent local inflammation (12,26,33).Inflammatory responses to ARTI have been best studied in rodent models. In the Cotton rat, a permissive host for replication of human adenovirus, pulmonary histopathology consists of early and late phases similar to that seen in human ARTI (15,39). The early phase consists primarily of accumulation of neutrophils, macrophages, and monocytes and develops within the first 24 h (60). The late phase, consisting mainly of lymphocytes, is apparent by day 5 (39, 60). In mice, a nonpermissive host for human adenovirus, adenovirus early gene

Immune responses to gene therapy vectors: influence on vector function and effector mechanisms

“…Several studies have shown that internalization of adenoviral vectors plays a crucial role in inducing the synthesis of proinflammatory cytokines. 5 These results further support the use of lower doses.…”

“…5 Interestingly, synthesis of adhesion molecules can also be induced by adenoviral infection. For instance, adenoviral infection of endothelial cells is followed by expression of adhesion molecules such as ICAM-1 and VCAM-1, 6 leading to increased leukocyte infiltration within transduced tissues.…”

Molecular basis of the inflammatory response to adenovirus vectors

“…In vitro, transduction of the macrophage cell line RAW264.7 with adenovirus vectors resulted in the rapid stimulation of TNF-a expression as early as 2 h post-transduction. 15 In these cells, adenovirus vector-induced TNF-a expression required vector internalization since chemical inhibition of endosome acidification and/or lysis attenuated TNF-a expression. 15 Combining this observation with the lack of transgene expression in macrophages would suggest that the triggering event might reside after endosomal escape but prior to nuclear localization of adenovirus vectors.…”

“…3,4 Advectors, in addition to inducing adaptive antiviral immunity, activate the innate arm of the immune system. 6,[12][13][14][15] The acute inflammation triggered by Advectors impacts gene transfer efficiency and causes significant morbidity in transduced hosts. 14,16 Our studies and others have characterized the innate response to Ad-vectors in vivo.…”

“…31 Activation of innate cells such as monocytes and resident macrophages is an essential component of the innate response to viral infection. In the lung, Zsengeller et al 15 showed the rapid accumulation of Ad5LacZ vectors in alveolar macrophages 10 min after vector Biology of adenovirus vector inflammation Q Liu and DA Muruve administration. This was associated with the upregulation of inflammatory cytokines and chemokines IL-6, TNF-a, MIP-2, and MIP-1a.…”